1. Field of the Invention
The present invention relates to electrical safety compliance test equipment, and in particular to:
(i) a system and method for verifying that detection circuitry in the test equipment will properly detect failure in a sample to be tested or device-under-test (DUT), and
(ii) a safety compliance test instrument that includes a built-in verification feature.
The verification system and method of the invention is preferably implemented by software that displays a series of user prompts upon start-up of the test instrument. The prompts guide the user through all of the steps needed to perform a verification test, including which leads need to be connected or disconnected.
2. Description of Related Art
Electrical safety compliance test instruments are used by manufacturers to test electrical products for hazards such as insulation or ground faults that could cause injuries to purchasers and users of the products. Conventional safety compliance tests include continuity, ground bond, AC and DC dielectric withstand or xe2x80x9chipot,xe2x80x9d insulation resistance, line leakage, and run tests. For convenience, it is common for safety compliance instruments to be capable of performing more than one of these tests.
If fail detection circuitry in the test equipment are not operating properly, the equipment may fail to detect defective products. As a result, it is critical that the ability of the fail detection circuitry to detect test failures be periodically verified. Such verification is conventionally accomplished through the use of external text boxes that can be connected to the test instrument in place of the sample to be tested, and that are used during verification to simulate a defective product and thereby verify instrument performance. However, verification test boxes are costly and inconvenient to store and use.
The main reason for using external test boxes is that they eliminate the need for the operator to make the necessary connections to simulate product failure. Generally, this simply involves establishing a short between the appropriate test terminals, and could be accomplished without the need for a test box by an operator having proper training and sufficient alertness. However, given the criticality of proper product testing, and human nature, manufacturers and safety inspectors are unwilling to rely on the operator alone, particularly with respect to instruments capable of performing multiple different types of safety compliance tests involving different lead configurations.
The system and method of the invention address this problem by providing built-in verification capabilities that permit manufactures of electrical products to satisfy safety agency requirements for verification, without the inconvenience and cost of external test boxes, by providing an interactive display system that instructs the equipment operator on how to connect the leads to perform verification for a particular test, and that ensures that the verification results will be properly interpreted. So long as the operator follows the instructions provided by the system and method of the invention, it is impossible for the operator to, for example, mistakenly use a continuity test lead configuration to verifying the functioning of hipot detectors.
This capability should not be confused with the capability of providing on-screen prompts that guide an operator in setting-up the safety compliance tests themselves, i.e., that instruct the operator on connecting leads to the sample to be tested, rather than on setting-up a verification test of the test circuitry. On-screen safety compliance test set-up prompts are disclosed in U.S. patent application Ser. No. 09/699,331, filed Oct. 31, 2000, and herein incorporated by reference.
In addition, the present invention is to be distinguished from fully automated safety compliance testing systems and methods in which set-up, testing, and verification is carried-out solely under computer control via a single pre-configured test interface to the device under test, rather than by having the operator switch connections for the various tests, such as disclosed in U.S. Pat. No. 5,861,882. Such systems, as explained in the abstract of U.S. Pat. No. 5,861,882, seek to dynamically reconfigure the test set up for different tests without hand rewiring, and thus lack the flexibility of discrete test instruments, while at the same costing far more.
Finally, the present invention is to be distinguished from devices having automated self-test functions, such as fire alarms, in which detectors are periodically checked for proper functions. The type of verification with which the present invention is concerned seeks not just to test a single component, but to simulate an actual test to determine whether failures can be properly detected. For example, it may be that the detector is functioning properly, but that there is a short elsewhere in the power circuitry that precludes proper functioning of the tester so that self-testing of a single component would not detect the error.
A specific example of safety compliance test equipment with self-test functions or circuitry, is disclosed in U.S. Pat. No. 5,481,194. As explained in the abstract of this patent, a xe2x80x9cbuilt-in test circuit tests whether the fault detection circuit is operating correctly.xe2x80x9d While useful in equipment that does not permit different test lead configurations, this type of fully automated self-test circuitry does not eliminate the need for the present invention in a multifunction tester having different test configurations, and which therefore requires either a test box or operator intervention during verification.
U.S. Pat. Nos. 6,091,188; 4,398,188; and 3,737,765 also disclose self-test circuits in ground circuit or high voltage monitoring systems, but the monitoring systems of these patents are permanently connected to the systems being monitored, and the self-tests are conducted automatically at regular intervals rather than in response to operator input.
U.S. Pat. No. Re. 31,864 is of interest for its disclosure of an appliance self-test feature in which the operator is prompted to participate in the self-test by pressing keys on a keyboard, although the operator is not prompted with respect to test lead configurations.
U.S. Pat. No. 3,829,842 is of interest for its disclosure of an controller self-test function that automatically adapts to the equipment being controlled, and that permits manual testing of controller functions.
U.S. Pat. Nos. 6,064,372 and 5,861,882 are cited as background for their general disclosures of menu-driven interfaces for test equipment. The equipment described in these patents lack self-test or test circuit verification functions.
Also by way of background, examples of test instruments having programmable displays suitable for carrying out the verification system and method of the invention, though not in the context of safety compliance test instruments, include the medical diagnostic instrument display disclosed in U.S. Pat. No. 5,056,059, the communications line test device disclosed in U.S. Pat. No. 5,808,920, voltage-current multimeter displays such as the one disclosed in U.S. Pat. No. 6,064,372, which eliminate the need for multiple buttons by including a touch screen, and oscilloscope displays, including the softkey controlled oscilloscope display described in U.S. Pat. No. 5,321,420.
Finally, examples of safety compliance test equipment displays that are especially suitable for implementing the invention include the scrolling displays integrated into the test instruments disclosed in U.S. patent application Ser. No. 09/699,331, cited above, and U.S. Pat. Nos. 6,054,865 and 6,011,398 (which correspond to instruments commercially available from Associated Research, Inc of Lake Forest, Ill.), or the test instrument disclosed in U.S. Pat. No. 5,101,160. It will of course be appreciated, however, that the system and method of the invention are not to be limited to any particular display or safety compliance test instrument.
It is a accordingly a first objective of the invention to provide a verification system and method that enables verification of a safety compliance instrument""s fail detection test circuitry without the need for an external verification box, and yet with minimal risk that an operator will set-up the verification test incorrectly.
It is a second objective of the invention to provide a safety compliance test instrument having a reduced risk that fail detector circuitry will give an incorrect reading due to operator error during testing.
It is a third objective of the invention to provide a test verification software that may easily be installed on existing safety compliance test instruments with programmable interactive displays.
These objectives of the invention are achieved, in accordance with the principles of a preferred embodiment of the invention, by providing a verification system and method in which prompts for set-up of individual verification tests are supplied through an interactive, menu-driven display which guides the operator through the proper set-up procedure and displays the results of the verification tests in a way that ensures that they will not be misinterpreted.
The objectives of the invention are further achieved by providing a safety compliance test instrument having a display capable of displaying menus and prompts, means by which an operator may input responses to displayed menus, and software for displaying a plurality of instrument verification menus, prompts, and messages concerning lead-configurations for, and results of, the instrument verification tests.
According to an especially preferred embodiment of the invention, the safety compliance instrument includes at least two different safety compliance tests to be verified, the at least two different safety compliance tests requiring different connections to a device under test. The tests may be selected from the group consisting of a continuity test, a ground test, a dielectric withstand test, and an insulation resistance test, and more specifically from the group consisting of a continuity test, a ground bond test, AC and DC dielectric withstand tests, and an insulation resistance test.
It will be appreciated by those skilled in the art that the verification system of the invention may be implemented on any test instrument having an interactive display capable of presenting a series of menus, and of having the operator select options presented by the menus, including instruments with full keyboards rather than softkeys, or with cursor control type inputs, as well as one or two line displays that require scrolling.
Although a particular type of safety compliance test instrument is described in detail herein, those skilled in the art will appreciate that the principles of the preferred embodiment of the invention may be applied to line leakage testers, run testers, and a variety of other test instruments capable of running multiple pre-programmed test sequences requiring multiple test lead configurations.